The present invention relates to a liquid repellent structure exhibiting high repellency with respect to liquids such as water, an organic solvent and oil, a method of producing the liquid repellent structure that ensures high productivity, a liquid ejection head using the liquid repellent structure and a stain-resistant protective film.
As for water repellent materials and surface structures obtained from such materials, a contact angle of at least 90° is obtained by using a fluorine-based material. However, a material and a structure exhibiting repellency with respect to a liquid having a low surface tension such as an organic solvent or oil have not been fully examined yet.
Most of the conventionally known repellent materials mainly exhibit repellency with respect to water (also called water repellency). Water repellent materials have been used for rain gear, household utensils such as kitchen utensils, industrial equipment, and the like.
A repellent material is industrially applied to an inkjet system with which finely divided ink droplets are ejected and sprayed onto and adhered to recording paper to perform recording. In the inkjet system, it is very important to form a repellent film around each ejection port in order to enhance the ejection performance.
A super-water-repellent polytetrafluoroethylene (PTFE) film formed by nickel eutectoid plating and having a contact angle in excess of 150° with respect to water has been realized as the water repellent material.
It is important to study both of the properties of a material (material having a low surface tension) and the surface structure in order to improve repellency and various studies have been conventionally made (see, for example, JP 2000-226570 A).
JP 2000-226570 A discloses a water repellent structure obtained by forming a water repellent film with a thickness of about 100 nm on the surface of an uneven surface structure that was formed by photolithography on a surface of a substrate.
In addition to the water repellent structure described in JP 2000-226570 A, also is known a method of forming a honeycomb structure by evaporating finely divided water droplets formed on the surface of a repellent polymer by condensation (see, for example, JP 2001-157574 A).
JP 2001-157574 A discloses a honeycomb structure obtained by casting a solution of a biodegradable polymer and an amphipathic polymer in a hydrophobic organic solvent onto a substrate in an atmosphere with a relative humidity of 50 to 95%, causing condensation on the surface of the cast solution while gradually evaporating the organic solvent, and evaporating finely divided water droplets generated by the condensation.
Honeycomb structures having excellent water repellency have also been proposed (see JP 2005-23122 A and H. Yabu, et al., “Superhydrophobic and Lipophobic Properties of Self-Organized Honeycomb and Pincushion Structures”, Langmuir 3, 8, 2005, 21, 3235-3237). The document of H. Yabu, et al. is hereinafter referred to simply as “Non-Patent Document 1”.